1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method therefor, and more particularly to a semiconductor device including a gate insulating film formed on a silicon substrate and a gate electrode formed on the gate insulating film, and a manufacturing method for the semiconductor.
2. Background Art
In recent years, the integration density of semiconductor integrated circuit devices has considerably increased. As such, devices such as transistors in MOS (Metal Oxide Semiconductor) semiconductor devices have been miniaturized and enhanced in performance. Especially, gate insulating films, which are a component of the MOS structure, have become thinner and thinner to accommodate the miniaturization, higher-speed operation, and lower-voltage operation of the transistors.
Gate insulating films have been traditionally formed of an SiO2 (silicon oxide) film. On the other hand, as gate electrodes have been miniaturized, the gate insulating films have been reduced in thickness. However, considerably reducing the thickness of a gate insulating film causes carriers (electrons and holes) to pass through the film, thereby increasing the tunneling current, or gate current. According to ITRS (International Technology Roadmap for Semiconductors) 2003, the 65 nm generation semiconductor devices, which are expected to become available in 2007, require gate insulating films having an equivalent oxide thickness of 0.9 nm–1.6 nm. However, when an SiO2 film is used as a gate insulating film, the gate leakage current due to the tunneling current exceeds the maximum permissible value, requiring a new material to be employed instead of the SiO2 film.
Research efforts have been made to use materials having a higher relative permittivity than SiO2 films for gate insulating films. High dielectric constant insulating films (hereinafter referred to as High-k films) gaining attention include HfO2 (hafnium oxide) films, HfAlOx (hafnium aluminate) films, and HfSiOx (hafnium silicate) films.
However, phase separation, crystallization, etc. are likely to occur with a High-k film, causing the problem of boron (B) in the gate electrode penetrating through the High-k film to the substrate and thereby changing the transistor threshold voltage considerably. To overcome this problem, a method is proposed for adding nitrogen (N) into the High-k film to prevent boron penetration (see M. A. Quevedo-Lopez et al., Applied Physics Letters, 2003, p. 4669–4670).
Adding nitrogen into the High-k film, however, leads to a large reduction in the drive power when a low voltage relative to the substrate is continuously applied to the gate electrode at a high temperature, which is referred to as negative bias temperature instability (NBTI). On the other hand, adding fluorine into the film improves reliability factors such as NBTI, but promotes boron penetration (see Dieter K. Schroder et al., Journal of Applied Physics, 2003, p. 1–18).
Thus, nitrogen and fluorine have opposite effects on the problems of boron penetration and NBTI. Therefore, simply adding both elements into the High-k film, as is conventionally done, cannot solve these problems.